We propose to use high pressure liquid chromatography in conjunction with a variety of physiologic techniques to investigate absorption and metabolism of various water-soluble vitamins. Emphasis will be directed at riboflavin, niacin and vitamin C. We plan to study absorption by the vascularly perfused small intestine, influx across the mucosal cell membrane and accumulation by isolated cells. The kinetics of uptake will be examined to determine characteristics of the brush border transport process. Cellular accumulation will be evaluated in normal and poisoned tissue to determine if each vitamin accumulates against an electrochemical gradient. The vascularly perfused small intestine will be used to determine whether vitamin is metabolized during absorption from the lumen to the vascular perfusate.